1. Field of the Invention
The present invention relates to a thin film magnetic head having at least an inductive magnetic transducer for recording and a method of manufacturing the same.
2. Description of the Related Art
In recent years, improvement in performance of a thin film magnetic head is demanded as the areal density of a magnetic recording medium (hereinbelow, simply called “recording medium”) such as a hard disk increases. As magnetic recording methods applied to a thin film magnetic head, for example, a longitudinal recording method in which the orientation of a signal magnetic field is set to an in-plane direction (longitudinal direction) of a recording medium and a perpendicular recording method in which the orientation of a signal magnetic field is set to a direction which perpendicularly crosses the face of a recording medium are known. At present, the longitudinal recording method is widely used. However, when a market trend accompanying improvement in areal density is considered, it is assumed that, in place of the longitudinal recording method, the perpendicular recording method will be regarded as a promising method in future for the following reason. The perpendicular recording method has advantages such that high linear recording density can be assured and a recorded recording medium is not easily influenced by thermal fluctuations.
As recording modes using the perpendicular recording method, for example, the following modes are proposed; (1) a mode of using a head (ring-type head) facing each other with a gap on one end side and are magnetically connected to each other on the other end side and a recording medium in which a main component has a single-layer configuration, and (2) a mode of using a head (single-pole type head) disposed perpendicular to a recording medium and a recording medium in which a main component has a two-layer configuration. Out of the modes, the mode of using the combination of the single-pole type head and the recording medium of the two-layer structure has a remarkably excellent resistance to thermal fluctuations. Consequently, attention is being paid to the mode as a mode which can realize improvement in the performance of the thin film magnetic head.
To improve the recording performance of the thin film magnetic head of the perpendicular recording method, for example, a sufficient amount of a magnetic flux has to be supplied to a main magnetic pole layer as the main path of a magnetic flux in the single-pole type head in order to assure intensity of a magnetic field for recording (perpendicular magnetic field) and to assure a stabilized recording operation.
A thin film magnetic head capable of addressing the demand is considered to have, for example, a main magnetic pole layer, an auxiliary magnetic pole layer of which one end face is recessed from an air bearing surface and which is disposed so as to face a part of the main magnetic pole layer, and a non-magnetic layer disposed so as to be sandwiched between the main magnetic pole layer and the auxiliary magnetic pole layer. By the main magnetic pole layer, non-magnetic layer, and auxiliary magnetic pole layer, a stacked structure is constructed. In the thin film magnetic head, in spite of the fact that the auxiliary magnetic pole layer is completely isolated from the main magnetic pole layer via the non-magnetic layer, the auxiliary magnetic pole layer plays the role of supplying a magnetic flux to the main magnetic pole layer in an auxiliary manner. Consequently, as compared with the case where only the main magnetic pole layer is provided and the auxiliary magnetic pole layer is not provided, an amount of the magnetic flux supplied to the main magnetic pole layer increases.
In the thin film magnetic head, for a reason of a manufacturing process, the front end position of the auxiliary magnetic pole layer (position on the side close to the air bearing surface) inevitably coincides with the flare point. The flare point is the position from which the width of the magnetic pole layer (including the main magnetic pole layer) as a path of a magnetic flux increases from a uniform width specifying the recording track width of a recording medium to a width larger than the uniform width. The flare point is one of important factors determining the recording performance of a thin film magnetic head.
However, when the method of manufacturing a thin film magnetic head introduced above is used, although there is an advantage from the viewpoint of supplying the magnetic flux to the main magnetic pole layer on the basis of the existence of the auxiliary magnetic pole layer, in some cases, it is feared that a normal recording operation is disturbed. From the viewpoint of properly setting the flare point, when the auxiliary magnetic pole layer is set too close to the air bearing surface, the perpendicular magnetic field distribution on the trailing side of the main magnetic pole layer may be disturbed by the influence of the magnetic flux concentrated on the area at the tip of the auxiliary magnetic pole layer.
To improve the recording performance of the thin film magnetic head of the perpendicular recording method, in addition to supply of a sufficient amount of the magnetic flux to the main magnetic pole layer as described above, there are mainly the following two important points in design of the main magnetic pole layer.
First, to increase the recording density, it is necessary to form at high precision a portion having a very small uniform width specifying the recording track width of a recording medium (hereinbelow, called “track width specifying portion”) in the main magnetic pole layer. Hitherto, the main magnetic pole layer is formed by, for example, forming a magnetic layer and patterning the magnetic layer so as to have a predetermined pattern shape by using the photolithography technique, etching technique, and the like. At the time of forming the main magnetic pole layer, high processing precision is requested to form the track width specifying portion.
Second, in order to suppress magnetic saturation and to supply a sufficient amount of a magnetic flux to the track width specifying portion, it is necessary to set a portion having a width larger than that of the track width specifying portion (hereinbelow, called “magnetic flux supply portion”) in the main magnetic pole layer close to the air bearing surface to a degree that excessive emission of the magnetic flux is not induced. The position of the front edge of the magnetic flux supply portion (the edge on the side close to the air bearing surface) specifies the position from which the main magnetic pole layer is widened from the track width specifying portion to the magnetic flux supply portion and is generally called “flare point”. The flare point is the position where the magnetic flux flowing from the magnetic flux supply portion to the track width specifying portion in the main magnetic pole layer is converged. From the viewpoint of supplying the magnetic flux into the track width specifying portion, the flare point is one of important factors to determine the recording performance of a thin film magnetic head.
The conventional method of manufacturing a thin film magnetic head has, however, a problem that, in spite of the necessity of high precision in formation of the track width specifying portion and proper setting of the flare point in order to improve the recording performance, it is difficult to realize both of the high precision and the proper setting for the following reason.
For example, at the time of forming a photoresist pattern necessary to form a main magnetic pole layer by selectively exposing a photoresist by using the photolithography technique, if the exposure pattern includes both of a very narrow area corresponding to the track width specifying portion and a wide area corresponding to the magnetic flux supply portion, the very narrow area and its peripheral area are excessively exposed due to the influence of reflection light generated at the time of exposure and there is a case that the exposed area expands. When the exposed area expands, precision in formation of the photoresist pattern deteriorates so that it becomes difficult to form the track width specifying portion at high precision. Moreover, the problem of the precision in formation of the track width specifying portion becomes more conspicuous the closer the flare point to the air bearing surface is and the higher the occupation ratio of the wide area in the very narrow area is. In the conventional techniques, therefore, the high precision in formation of the track width specifying portion and the proper setting of the flare point have the relation of a trade-off. To prove practical use and future potential of the perpendicular recording method and spread a hard disk drive of a large capacity using the method, it is urgently needed to solve the problems and realize improvement in the recording performance.
There are already some prior arts directed to improve the recording performance of a thin film magnetic head of the perpendicular recording method.
Concretely, first, Japanese Unexamined Patent Publication (JP-A) No. 6-274811 discloses a method of realizing high-density recording by properly selecting a material of a head. Second, JP-A No. 2002-197611 discloses a method of forming a main magnetic pole layer by plating so as to have a predetermined shape by properly setting the shape of a yoke layer. Third, JP-A No. 2002-197615 discloses a method of improving precision in formation of a main magnetic pole layer by forming the main magnetic pole layer on a flat surface. Fourth, JP-A No. 6-180810 discloses a method of improving signal quality of a reproduction waveform by avoiding the phenomenon of unnecessary concentration of a magnetic flux by notching a portion facing a main magnetic pole in a return yoke layer.
From the above-described methods, however, no guideline is obtained regarding realization of high precision in formation of a main magnetic pole layer and proper setting of a flare point which are pointed out in the above.